In recent years, with an increase of an amount of communication and information, interest has focused on radio communication technology using a high-frequency band which allows transmission of large amount of information at high speeds. Especially, in a high-frequency band of 60 GHz band, since no license is required to the frequency band of 2.5 GHz for one transmitter, communication is possible at a high speed of 1 Gbps or more by using the above-mentioned transmitter.
Since transmission loss of a free space increases in a radio communication apparatus using a high-frequency band, high-gain antennas have been used to increase the communication distance. Since a half value width of a radiation pattern is typically narrow in the high-gain antenna, the alignment of antennas is extremely important. Specifically, when the alignment of the high-gain antennas is determined, communication is performed while varying the radiation direction of radio signals to find out the radiation direction which maximizes the reception power. The radiation direction that is found out is used to achieve excellent communication. Further, even when the alignment of the antennas is deviated, it is possible to automatically recover excellent communication by performing the same processing.
FIG. 12 is a schematic diagram schematically showing a state in which alignment of antennas is automatically controlled when two radio communication apparatuses communicate with each other. First, one radio communication apparatus 50 transmits radio signals to the other radio communication apparatus 51 while changing the radiation direction of the radio signals to be sent from the antennas in all directions. On the other hand, the other radio communication apparatus 51 that receives the radio signals from the radio communication apparatus 50 extracts reception power and an S/N as measurement values from the radio signals that the radio communication apparatus 51 receive, and transmits the measurement values that are extracted to the radio communication apparatus 50 which is the transmission source. The radio communication apparatus 50 calculates the radiation direction which makes the S/N in the radio communication apparatus 51 maximum based on the measurement values received from the radio communication apparatus 51 which is the transmission destination, and controls the radiation direction of the radio signals to be transmitted from the antennas according to the radiation direction that is calculated.
As shown in FIG. 12, as one method of controlling the radiation direction of radio signals sent from the antennas of the transmitter forming the radio communication apparatus 50, a so-called array antenna including a plurality of antenna elements is used. The array antenna controls the phase of the radio signal sent from each of the antenna elements, to control the radiation direction of the radio signals. The array antenna here is an antenna in which a plurality of antenna elements are arranged in array, and is typically formed as a phased array antenna that is capable of controlling phases of radio signals to be sent.
As a method of forming a transmitter including a phased array antenna and controlling phases of radio signals, FIGS. 13 to 15 show configuration examples of three kinds of transmitters. FIG. 13 shows a configuration of the transmitter typically used as a related art of the present invention in the transmitter controlling phases of radio signals. In a transmitter 52 shown in FIG. 13, radio signals generated by converting frequencies after up-converting I and Q baseband signals in a quadrature modulator 54 by a local signal after being amplified by a local signal amplifier 53 are distributed into the number corresponding to h (h is an integer) transmission antennas 57-1 to 57-h forming the array antenna, and the phase of each of the radio signals is changed and controlled to an appropriate value by h radio signal phase shifters 55-1 to 55-h provided in the respective paths that are distributed.
After that, h radio signals whose phases are changed and controlled by the respective radio signal phase shifters 55-1 to 55-h are amplified by transmission amplifiers 56-1 to 56-h and then sent from transmission antennas 57-1 to 57-h, respectively.
In the case of the configuration shown in the transmitter 52 shown in FIG. 13, each of the radio signal phase shifters 55-1 to 55-h needs to be formed by a high-frequency band, and it is difficult to form a wide band phase shifter.
Meanwhile, FIG. 14 shows a configuration of a transmitter disclosed in a non-patent literature 1 as a related art of the present invention in a transmitter for controlling phases of radio signals. In a transmitter 58 shown in FIG. 14, a local signal after being amplified by a local signal amplifier 59 is first distributed into the number corresponding to h (h is an integer) transmission antennas 63-1 to 63-h forming the array antenna, and the phases of the local signals are changed and controlled to appropriate values by h local signal phase shifters 60-1 to 60-h provided in the respective paths that are distributed.
After that, I and Q baseband signals are up-converted by quadrature modulators 61-1 to 61-h by the local signals whose phases are changed and controlled to generate radio signals. Then, the signals are amplified by respective transmission amplifiers 62-1 to 62-h, and then sent from transmission antennas 63-1 to 63-h, respectively.
In the case of the configuration shown in the transmitter 58 shown in FIG. 14, each of the local signal phase shifters 60-1 to 60-h converts and controls the phase at the local signal level. This requires a plurality of quadrature modulators. However, it is not necessary to form a wide band phase shifter. Thus, it is possible to form the transmitter more easily than the case of the transmitter 52 shown in FIG. 13.
Further, FIG. 15 shows a configuration of a transmitter disclosed in a patent literature 1 which is filed by the applicants of the present invention as a related art of the present invention in a transmitter controlling phases of radio signals. A transmitter 64 shown in FIG. 15 distributes each path of I and Q baseband signals into the number corresponding to h (h is an integer) transmission antennas 69-1 to 69-h forming the array antenna, and the phases of the respective baseband signals are changed and controlled to appropriate values by h baseband signal phase shifters 66-1 to 66-h provided in the respective paths that are distributed.
After that, the baseband signals after the phases are changed and controlled are up-converted by respective quadrature modulators 67-1 to 67-h by a local signal amplified by a local signal amplifier 65 to generate radio signals. Then, the baseband signals are amplified by respective transmission amplifiers 68-1 to 68-h, and then sent from the transmission antennas 69-1 to 69-h, respectively.
In the case of the configuration shown in the transmitter 64 in FIG. 15, the conversion control of the phases is performed at the baseband signal level in each of the baseband signal phase shifters 66-1 to 66-h. Thus, as is similar to the configuration of the transmitter 58 shown in FIG. 14, although a plurality of quadrature modulators are required, there is no need to form a wide band phase shifter. Since there is no need to form a wide band phase shifter, it is possible to form the transmitter more easily than the case of the transmitter 52 shown in FIG. 13.